i wouldn't think that the fact that your using a mac would have any effect on the way your amp works. any computer that is using a standard audio card (integrated into the motherboard) is most likely to just put out the same type of sound in 2 separate channels (obviously there are motherboard with surround sound built in but for the sake of this conversation lets just assume). Anyway my point is that mac/pc/whatever has no bearing on how your amp works. if you have a 2 channel amp, there is a good chance you are only going to be able to fade left to right, since you only have 2 channels in and 2 channels out. If you have a 4 channel amp (depending on the amp) you should be able to get front/back - left/right fade. I would also suggest posting this in the car audio forum, you may get better responses there.